1. Field of the Invention
The present invention relates to a driving circuit for a semiconductor laser diode (LD), in particular, the invention relates to a driver to suppress the degradation of the quality of the optical output.
2. Related Prior Art
Various driver circuits for a semiconductor laser diode (herein after denoted as LD) have been known. The LD shows a time lag from the injection of the carriers into the active laser thereof to the emission of the coherent light, which corresponds to the resonance frequency of the LD. Accordingly, when the LD is driven with a high frequency signal, the interference may occur between data due to the resonance of the signal applied thereto and the time lag of the LD. A Japanese Patent published as JP-S60-187075A has disclosed a typical conventional driver for the LD to compensate the frequency response of the LD where the circuit provides an additional circuit connected in parallel to the LD. The circuit disclosed in the prior patent includes a series circuit of a capacitor and a resistor, a parallel circuit of a diode and a capacitor, or a combination of a series circuit of a resistor and a capacitor and a parallel circuit of a diode and a capacitor. Such additional circuit may compensate the high frequency response of the LD.
However, the conventional driver carries out the compensation for the frequency response of the LD by a combination of resistor, capacitor, and diode each showing constant value. This is due to a reason that such elements applicable in the compensation circuit are necessary to show an excellent high frequency characteristic.
However, the LD itself and elements used in the driving circuit have inherently scattered characteristics, and it is necessary to replace elements to follow the frequency response of respective LDs when the circuit applies such elements with the constant value. Moreover, the LD generally shows strong temperature dependence in its frequency response. Accordingly, such circuit elements occasional is unable to compensate the frequency response of the LD.
The present invention is to provide a driving circuit for the LD, in which the scattering of the frequency characteristic of respective LDs and the temperature dependence of the LD may be compensated enough.